A variety of liquid dentifrices have previously been proposed in the art, such as for example, those disclosed in Japanese Patent Publication Nos. 36599/1970 and 15443/1980, but few liquid dentifrices have been a commercial success. The major problem is low applicability properties in that when liquid dentifrice is applied to a toothbrush, it will quickly soak through the bristles and flow down from the brush. Another problem of prior art liquid dentifrices is their excess flow or extrudability in that in dispensing the liquid dentifrice from a plastic bottle or similar container, an excess of liquid dentifrice is often applied to the toothbrush.
For these and other reasons, toothpastes have enjoyed the most widespread use while some gel dentifrices having a relatively low viscosity (200 to 500 poise) are used as disclosed in Japanese Patent Application Kokai No. 75412/1985 and 75413/1985, for example. Toothpastes and gel dentifrices are less satisfactory with respect to dispersion in the mouth and ease of washing of the toothbrush after use. For instance, most toothpastes are rather difficult to wash away because some deposits are left adhered to the bristles. In this respect, the liquid dentifrice has a hygienic advantage in that the toothbrush is easily washed clean after use. The use of a liquid dentifrice is recommended from the aspects of quick dispersion and easy rinsing of the toothbrush. It is, therefore, desired to solve the poor applicability of liquid dentifrice.
Most prior art liquid dentifrices are free of abrasive. However, it is desirable to blend abrasive in a liquid dentifrice to ensure a stain removing or cleaning power. To this end, the abrasive has to be dispersed in the liquid dentifrice in a stable manner. One prior art approach is to blend xanthane gum for a stable dispersion of the abrasive as disclosed in Japanese Patent Publication No. 36599/1970.
The inventors have found that a liquid dentifrice composition containing an abrasive in an effective amount to provide a cleaning power, say 5 to 40% by weight of the composition, lowers its fluidity with the lapse of time. Although the liquid dentifrice is normally prepared to have a low viscosity, the abrasive blended therein causes the liquid dentifrice to have a lower fluidity with time and eventually lose fluidity after long term storage.
It is, therefore, desired to prevent a liquid dentifrice composition having abrasive blended therein from exhibiting a lowered fluidity with time so that the liquid dentifrice will maintain a soft flow even after long term storage.